Active regions with compatible dielectric layers

ABSTRACT

A method to form a semiconductor structure with an active region and a compatible dielectric layer is described. In one embodiment, a semiconductor structure has a dielectric layer comprised of an oxide of a first semiconductor material, wherein a second (and compositionally different) semiconductor material is formed between the dielectric layer and the first semiconductor material. In another embodiment, a portion of the second semiconductor material is replaced with a third semiconductor material in order to impart uniaxial strain to the lattice structure of the second semiconductor material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/523,105, filed on Sep. 18, 2006, the entire contents of which arehereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The invention is in the field of Semiconductor Structures.

2) Description of Related Art

For the past several decades, semiconductor devices such as Metal OxideSemiconductor Field-Effect Transistors (MOS-FETs) have been fabricatedusing doped crystalline silicon for active regions, e.g. channelregions, and amorphous silicon dioxide for dielectric regions, e.g. gatedielectric layers. The beauty of the silicon/silicon dioxide pairing isthat the silicon dioxide can be formed directly on the surface of acrystalline silicon substrate via heating the substrate in the presenceof oxygen. The process is very controllable and can reliably providesilicon dioxide films as thin as 2-3 monolayers thick.

In the drive for ever-faster semiconductor devices, however, it may bedesirable to utilize a channel material other than crystalline silicon.One caveat is that very few other semiconductor materials, if any, formas compatible a surface amorphous oxide layer as does the crystallinesilicon/silicon dioxide pairing. This has made the utilization ofchannel materials other than silicon quite daunting. Thus, a method toform active regions with compatible dielectric layers, and the resultantstructures, is described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B illustrate cross-sectional views representing semiconductorstructures having active regions with compatible dielectric layers, inaccordance with an embodiment of the present invention.

FIGS. 2A-N illustrate cross-sectional views representing the formationof a planar MOS-FET having active regions with compatible dielectriclayers, in accordance with an embodiment of the present invention.

FIGS. 3A-C illustrate cross-sectional views representing the formationof a tri-gate MOS-FET having active regions with compatible dielectriclayers, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

A process for fabricating semiconductor devices, and the resultantdevices, is described. In the following description, numerous specificdetails are set forth, such as specific dimensions and chemical regimes,in order to provide a thorough understanding of the present invention.It will be apparent to one skilled in the art that the present inventionmay be practiced without these specific details. In other instances,well-known processing steps, such as patterning steps or wet chemicalcleans, are not described in detail in order to not unnecessarilyobscure the present invention. Furthermore, it is understood that thevarious embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Disclosed herein are semiconductor structures having active regions withcompatible dielectric layers and methods to form the same. Controlledthermal or native growth of an oxide, via consumption of the top surfaceof a semiconductor substrate in an oxidation process, can provide areliable dielectric layer. However, it may be desirable to retain thereliable dielectric layer, yet replace the portion of the semiconductorsubstrate directly under the reliable dielectric layer with a differentsemiconductor material. This subsequent replacement of a portion of thesemiconductor substrate with a different semiconductor material directlybelow the dielectric layer may enable the formation of a new activeregion with a reliable dielectric layer. Thus, a structure may be formedwherein a dielectric layer comprising an oxide of a first semiconductormaterial is retained directly above a second, and different,semiconductor material. This process and the resulting structure can beparticularly beneficial in cases where the oxide of the secondsemiconductor material has inferior characteristics to the oxide of thefirst semiconductor material, but incorporation of the secondsemiconductor material is nonetheless desirable. Furthermore, a portionof the second semiconductor material may be replaced with a thirdsemiconductor material in order to impart uniaxial strain to the latticestructure of the second semiconductor material. The combination ofincorporating an optimal semiconductor material to form an active regionand applying uniaxial strain to that active region can lead to increasedcharge carrier mobility in the channel region of a semiconductor device.Thus, optimization of high performance semiconductor devices may beachieved.

The controlled consumption of the top surface of a semiconductorsubstrate via an oxidation process can provide a reliable (i.e. uniformthickness and consistent composition) dielectric layer on the surface ofthat substrate. For example, thermal or native growth of silicon dioxideon the surface of a crystalline silicon substrate provides a reliabledielectric layer as thin as 3-10 Angstroms (i.e. 1-3 monolayers). Theresulting oxide layer may be used as a gate dielectric layer, or acomponent thereof, in a semiconductor device. In accordance with anembodiment of the present invention, a silicon dioxide layer is formedon the surface of a crystalline silicon substrate by heating thecrystalline silicon substrate in the presence of an oxidizing agent,such as O₂, H₂O, or O₃. In accordance with an alternative embodiment ofthe present invention, a native layer of silicon dioxide is formed uponexposure of a crystalline silicon substrate to a water pulse in anatomic layer deposition (ALD) chamber. A bi-layer dielectric layer canbe formed by depositing a layer of a high-K dielectric material directlyabove the native silicon dioxide layer.

In some applications, a crystalline silicon substrate may not be themost desirable material for use as an active region (e.g. a channelregion) in a semiconductor device. For example, in accordance with anembodiment of the present invention, it is desirable to use germanium asthe channel material in a P-type device, while it is desirable to use aIII-V material as the channel material in an N-type device. In anotherembodiment, one of germanium or a III-V material is used for both theP-type device and the N-type device. By incorporating these channelmaterials into such devices, the hole mobility and the electronmobility, respectively, may be optimized for improved deviceperformance. However, the oxidation of the surfaces of germanium andIII-V materials tends to provide oxide layers that are unstable and/ornon-uniform in thickness or composition. It may therefore be desirableto combine a semiconductor material with an oxide layer of a differentsemiconductor material. Thus, in accordance with an embodiment of thepresent invention, a semiconductor material that would otherwise providean inferior oxide layer is combined with a reliable oxide layer, whereinthe oxide layer is an oxide of a different semiconductor material.

In order to provide a semiconductor structure comprising a secondsemiconductor material in combination with an oxide layer of a firstsemiconductor material, a replacement approach may be utilized. Ineffect, the oxide layer may be formed above a first semiconductormaterial, a portion of which is then removed to form a trench betweenthe oxide layer and the first semiconductor material. A secondsemiconductor material may then be formed in the trench. Thus, inaccordance with an embodiment of the present invention, a portion of asemiconductor substrate comprised of a first semiconductor material isreplaced with a second semiconductor material (i.e. an active region)directly between a pre-formed oxide layer and the semiconductorsubstrate.

A semiconductor region formed on or in a crystalline semiconductormaterial may impart a strain to the crystalline semiconductor material,and hence may be a strain-inducing semiconductor region, if the latticeconstant of the semiconductor region is different from the latticeconstant of the crystalline semiconductor material. The latticeconstants are based on the atomic spacings and the unit cellorientations within each of the semiconductor region and the crystallinesemiconductor material. Thus, a semiconductor region comprisingdifferent species of lattice-forming atoms than the crystallinesemiconductor material may impart a strain to the crystallinesemiconductor material. For example, in accordance with an embodiment ofthe present invention, a semiconductor region that comprises onlysilicon lattice-forming atoms imparts a strain to a crystallinesemiconductor material comprised of germanium lattice-forming atoms.Furthermore, a semiconductor region comprising the same species oflattice-forming atoms as the crystalline semiconductor material, butwherein the species of lattice-forming atoms are present in differentstoichiometric concentrations, may impart a strain to the crystallinesemiconductor material. For example, in accordance with an embodiment ofthe present invention, a semiconductor region that comprisesSi_(x)Ge_(1-x) lattice-forming atoms (where 0<x<1) imparts a strain to acrystalline semiconductor material comprised of Si_(y)Ge_(1-y)lattice-forming atoms (where 0<y<1, and x≠y).

As an example of an embodiment of the present invention, FIGS. 1A-Billustrate cross-sectional views representing semiconductor structureshaving active regions with compatible dielectric layers. Referring toFIG. 1A, a semiconductor structure 100 is comprised of a substrate 102,which is comprised of a first semiconductor material. An active region104 is above substrate 102 and the active region is comprised of asecond semiconductor material. In accordance with an embodiment of thepresent invention, the composition (i.e. the atomic make-up) of thesecond semiconductor material is different for that of the firstsemiconductor material. A dielectric layer 106 is directly above activeregion 104 and may comprise a layer of oxide of the first semiconductormaterial. A conductive region 108 is above dielectric layer 106, whichisolates conductive region 108 from active region 104.

Substrate 102 may comprise any semiconductor material that can withstanda manufacturing process. In an embodiment, substrate 102 is comprised ofa crystalline silicon or silicon/germanium layer doped with a chargecarrier, such as but not limited to phosphorus, arsenic, boron or acombination thereof. In one embodiment, the concentration of siliconatoms in substrate 102 is greater than 97%. In another embodiment,substrate 102 is comprised of an epitaxial layer grown atop a distinctcrystalline substrate, e.g. a silicon epitaxial layer grown atop aboron-doped bulk silicon mono-crystalline substrate. Substrate 102 maycomprise an insulating layer in between a bulk crystal substrate and anepitaxial layer to form, for example, a silicon-on-insulator substrate.In an embodiment, the insulating layer is comprised of a materialselected form the group consisting of silicon dioxide, silicon nitride,silicon oxy-nitride or a high-k dielectric layer.

Active region 104 may comprise any semiconductor material in whichcharges can migrate. In an embodiment, active region 104 is comprised ofa III-V material such as, but not limited to, gallium nitride, galliumphosphide, gallium arsenide, indium phosphide, indium antimonide, indiumgallium arsenide, aluminum gallium arsenide, indium gallium phosphide ora combination thereof. In another embodiment, active region 104 iscomprised of germanium or silicon/germanium with an atomic concentrationof germanium atoms greater than 5%. Active region 104 may incorporatecharge-carrier dopant impurity atoms. In one embodiment, active region104 is a crystalline silicon/germanium active region of thestoichiometry Si_(x)Ge_(1-x), where 0≦x≦1, and the charge-carrier dopantimpurity atoms are selected from the group consisting of boron, arsenic,indium or phosphorus. In another embodiment, active region 104 iscomprised of a III-V material and the charge-carrier dopant impurityatoms are selected from the group consisting of carbon, silicon,germanium, oxygen, sulfur, selenium or tellurium.

Dielectric layer 106 may comprise any dielectric material suitable toinsulate a conductive region 108 from active region 104. Furthermore,dielectric layer 106 may comprise a layer of oxide of a semiconductormaterial different than that of the semiconductor material of activeregion 104. In an embodiment, dielectric layer 106 is comprised of anoxide of a semiconductor material. In one embodiment, dielectric layer106 is comprised of silicon dioxide or silicon oxy-nitride. In anembodiment, dielectric layer 106 is comprised of an oxide layer of thesemiconductor material of substrate 102. In a specific embodiment,substrate 102 is comprised of silicon and dielectric layer 106 iscomprised of silicon dioxide or silicon oxy-nitride. In an embodiment,dielectric layer 106 is comprised of an oxide layer that is directlyabove active region 104. In one embodiment, dielectric layer 106 iscomprised of an oxide layer of the semiconductor material of substrate102, active region 104 is comprised of a semiconductor materialdifferent from the semiconductor material of substrate 102, and theoxide layer of dielectric layer 106 is directly on the top surface ofactive region 104. In a specific embodiment, dielectric layer 106 iscomprised of a silicon dioxide or silicon oxy-nitride, substrate 102 iscomprised of silicon, and active region 104 is comprised of germanium ora III-V material. Alternatively, dielectric layer 106 may be comprisedof a high-K dielectric layer. In one embodiment, the high-K dielectriclayer is selected from the group consisting of hafnium oxide, hafniumsilicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalumoxide, barium strontium titanate, barium titanate, strontium titanate,yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zincniobate or a combination thereof.

Conductive region 108 may comprise any material suitable to conduct acurrent. In an embodiment, conductive region 108 is comprised of dopedpolycrystalline silicon. In another embodiment, conductive region 108 iscomprised of a metal layer such as, but not limited to, metal nitrides,metal carbides, metal silicides, hafnium, zirconium, titanium, tantalum,aluminum, ruthenium, palladium, platinum, cobalt, nickel or conductivemetal oxides, e.g. ruthenium oxide.

Referring to FIG. 1B, additional features useful for the fabrication ofa semiconductor device 110 may be incorporated into semiconductorstructure 100. A pair of tip extensions 112 are formed in active region104 and are separated by a channel region 114, which comprises a portionof active region 104. Conductive region 108 may be a gate electrode, thetop surface of which may be protected by a gate electrode protectionlayer 116 and the sidewalls of which are protected by a pair of gateisolations spacers 118. The pair of gate isolation spacers 116 is abovethe pair of tip extensions 112. A pair of source/drain regions 120 isformed in active region 104 on either side of gate isolation spacers118. The pair of source/drain regions 120 may be raised above the topsurface of active region 104, as depicted in FIG. 1B. Dielectric layer106 may be a gate dielectric layer and may be comprised of two distinctdielectric layers, a lower layer 106A and an upper layer 106B, alsodepicted in FIG. 1B.

The pair of tip extensions 112 may comprises portions of active region104 that incorporate charge-carrier dopant impurity atoms. In oneembodiment, active region 104 is a crystalline silicon/germanium activeregion of the stoichiometry Si_(x)Ge_(1-x), where 0≦x≦1, and thecharge-carrier dopant impurity atoms are selected from the groupconsisting of boron, arsenic, indium or phosphorus. In anotherembodiment, active region 104 is comprised of a III-V material and thecharge-carrier dopant impurity atoms are selected from the groupconsisting of carbon, silicon, germanium, oxygen, sulfur, selenium ortellurium.

Gate electrode protection layer 116 and the pair of gate isolationspacers 118 may comprise any materials suitable to isolate gateelectrode. The same species of material, however, need not be used forboth gate electrode protection layer 116 and gate isolation spacers 118.In an embodiment, gate electrode protection layer 116 and gate isolationspacers 118 are comprised of insulating materials. In a particularembodiment, gate electrode protection layer 116 and gate isolationspacers 118 are comprised of a material selected from the groupcomprising silicon dioxide, silicon oxy-nitride, carbon-doped siliconoxide, silicon nitride, carbon-doped silicon nitride or a combinationthereof.

The pair of source/drain regions 120 may comprises portions of activeregion 104 that incorporate charge-carrier dopant impurity atoms. In oneembodiment, active region 104 is a crystalline silicon/germanium activeregion of the stoichiometry Si_(x)Ge_(1-x), where 0≦x≦1, and thecharge-carrier dopant impurity atoms are selected from the groupconsisting of boron, arsenic, indium or phosphorus. In anotherembodiment, active region 104 is comprised of a III-V material and thecharge-carrier dopant impurity atoms are selected from the groupconsisting of carbon, silicon, germanium, oxygen, sulfur, selenium ortellurium. Alternatively, the pair of source/drain regions 120 maycomprise a semiconductor material that is different from thesemiconductor material of active region 104. In an embodiment, thelattice-constant of the semiconductor material of source/drain region isdifferent from the lattice-constant of the semiconductor material ofactive region 104 and, thus, the pair of source/drain regions 120 is apair of uniaxial strain-inducing source/drain regions. In oneembodiment, active region 104 is comprised of Si_(x)Ge_(1-x) and thepair of source/drain regions 120 is comprised of Si_(y)Ge_(1-y) where0≦x, y≦1 and x≠y. In another embodiment, active region 104 is comprisedof Al_(x)Ga_(1-x)As, In_(x)Ga_(1-x)As, In_(x)Ga_(1-x)P orAl_(1x)In_(1-x)Sb and the pair of source/drain regions 120 is comprisedof Al_(y)Ga_(1-y)As, In_(y)Ga_(1-y)As, In_(y)Ga_(1-y)P orAl_(y)In_(1-y)Sb, respectively, where 0≦x, y≦1 and x≠y.

Dielectric layer 106 may be comprised of two distinct dielectric layers,a lower layer 106A and an upper layer 106B. In an embodiment, lowerlayer 106A is comprised of comprised of an oxide of a semiconductormaterial. In one embodiment, lower layer 106A is comprised of silicondioxide or silicon oxy-nitride. In an embodiment, lower layer 106A iscomprised of an oxide layer of the semiconductor material of substrate102. In a specific embodiment, substrate 102 is comprised of silicon andlower layer 106A is comprised of silicon dioxide or silicon oxy-nitride.In an embodiment, lower layer 106A is comprised of an oxide layer thatis directly above active region 104. In one embodiment, lower layer 106Ais comprised of an oxide layer of the semiconductor material ofsubstrate 102, active region 104 is comprised of a semiconductormaterial different from the semiconductor material of substrate 102, andlower layer 106A is directly on the top surface of active region 104. Ina specific embodiment, lower layer 106A is comprised of a silicondioxide or silicon oxy-nitride, substrate 102 is comprised of silicon,and active region 104 is comprised of germanium or a III-V material. Inan embodiment, upper layer 106B is comprised of silicon dioxide orsilicon oxy-nitride. In an alternative embodiment, upper layer 106B iscomprised of a high-K dielectric layer. In one embodiment, the high-Kdielectric layer is selected from the group consisting of hafnium oxide,hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate,tantalum oxide, barium strontium titanate, barium titanate, strontiumtitanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide,lead zinc niobate or a combination thereof. In a particular embodiment,semiconductor substrate 102 is comprised of silicon, lower layer 106A iscomprised of silicon dioxide or silicon oxy-nitride, and upper layer106B is comprised of a high-K dielectric layer.

Semiconductor structures having active regions with compatibledielectric layers may be used to form semiconductor devices. In oneembodiment, the semiconductor device is a planar MOS-FET, a memorytransistor or a micro-electronic machine (MEM). In another embodiment,the semiconductor device is a non-planar device, such as a tri-gate orFIN-FET transistor, an independently-accessed double-gated MOS-FET, or agate-all-around MOS-FET with a nanowire channel. FIGS. 2A-N illustratecross-sectional views representing the formation of a planar MOS-FEThaving active regions with compatible dielectric layers, in accordancewith an embodiment of the present invention. In one embodiment, such aprocess enables the formation of a high quality dielectric layer(comprising an oxide of a first semiconductor material) on an activeregion (i.e. the second, replacement semiconductor material) comprisedof a semiconductor material that does not typically yield an oxide ofhigh quality. As will be appreciated in the typical integrated circuit,both N- and P-channel transistors may be fabricated in a singlesubstrate or epitaxial layer to form a CMOS integrated circuit.

Referring to FIG. 2A, a gate dielectric layer 206 is formed above asubstrate 202. Substrate 202 may comprise any material discussed inassociation with substrate 102 from FIGS. 1A-B. Likewise, gatedielectric layer 206 may comprise any material discussed in associationwith dielectric layer 106 from FIG. 1A. Gate dielectric layer 206 may beformed from an oxide of substrate 202 by any technique suitable toprovide a reliable (i.e. uniform composition and thickness) dielectriclayer above the top surface of substrate 202. In accordance with anembodiment of the present invention, gate dielectric layer 206 is formedby consuming a portion of the top surface of substrate 202. In oneembodiment, gate dielectric layer 206 is formed by oxidizing the topsurface of substrate 202 to form an oxide layer comprised of an oxide ofthe semiconductor material of substrate 202. In a particular embodiment,gate dielectric layer 206 is formed by heating substrate 202 in thepresence of an oxidizing agent, such as O₂, H₂O or O₃, until a desiredthickness of an oxide layer is formed. In a specific embodiment,substrate 202 is comprised of silicon, gate dielectric layer 206 iscomprised of a layer of silicon dioxide, the formation of the layer ofsilicon dioxide is carried out at a temperature in the range of 600-800degrees Celsius for a duration in the range of 1 minute-1 hour, and thelayer of silicon dioxide is formed to a thickness in the range of 5-15Angstroms. In another embodiment, gate dielectric layer 206 is formed byoxidizing the top surface of substrate 202 in the presence of anitrogen-containing gas to form an oxy-nitride layer comprised of anoxy-nitride of the semiconductor material of substrate 202. In aparticular embodiment, gate dielectric layer 206 is formed by heatingsubstrate 202 in the presence of an oxidizing agent, such as O₂, H₂O orO₃, and ammonia until a desired thickness of an oxy-nitride layer isformed. In a specific embodiment, substrate 202 is comprised of silicon,gate dielectric layer 206 is comprised of a layer of siliconoxy-nitride, the formation of the layer of silicon oxy-nitride iscarried out at a temperature in the range of 600-800 degrees Celsius fora duration in the range of 1 minute-1 hour, and the layer of siliconoxy-nitride is formed to a thickness in the range of 5-15 Angstroms. Inan alternative embodiment, gate dielectric layer 206 is formed by adeposition process. In one embodiment, the deposition process isselected from the group consisting of a chemical vapor depositionprocess, an atomic layer deposition process or a physical vapordeposition process.

Referring to FIG. 2A′, gate dielectric layer 206 may be comprised of twodistinct dielectric layers, a lower layer 206A and an upper layer 206B.Lower layer 206A and upper layer 206B of gate dielectric layer 206 maycomprise any material discussed in association with lower layer 106A andupper layer 106B from FIG. 1B. In accordance with an embodiment of thepresent invention, subsequent to the formation of lower layer 206Acomprised of an oxide or oxy-nitride layer above substrate 202 (asdiscussed above), upper layer 206B may be formed above lower layer 206A.Upper layer 206B may be formed by any technique suitable to provide areliable (i.e. uniform composition and thickness) dielectric layer abovethe top surface of lower layer 206A. In an embodiment, upper layer 206Bis formed by a deposition process. In one embodiment, the depositionprocess is selected from the group consisting of a chemical vapordeposition process, an atomic layer deposition process or a physicalvapor deposition process. In an alternative embodiment, gate dielectriclayer 206 comprising two distinct dielectric layers, i.e. lower layer206A and an upper layer 206B, may be formed in a single process step(i.e. in a single reaction chamber without requiring multipleintroductions of substrate 202 into the reaction chamber). In oneembodiment, a native layer of oxide (i.e. lower layer 206A) is formedupon exposure of substrate 202 to a water pulse in an atomic layerdeposition (ALD) chamber. An upper layer 206B of a dielectric materialmay then be deposited above the native oxide layer by a sequencing ofdielectric precursor introductions into the ALD chamber. In a particularembodiment, substrate 202 is comprised of silicon, lower layer 206A is anative silicon dioxide layer with a thickness in the range of 3-10Angstroms, and upper layer 206B is a high-K dielectric layer selectedfrom the group consisting of hafnium oxide, hafnium silicate, lanthanumoxide, zirconium oxide, zirconium silicate, tantalum oxide, bariumstrontium titanate, barium titanate, strontium titanate, yttrium oxide,aluminum oxide, lead scandium tantalum oxide, lead zinc niobate or acombination thereof.

A gate electrode 208 may then be formed above gate dielectric layer 206,as depicted in FIG. 2B. For illustrative purposes, gate dielectric layer206 is depicted as a single layer film (i.e. as illustrated in FIG. 2A),but it should be understood that it may comprise more than one layer, asdiscussed in association with FIG. 2A′. Gate electrode 208 may compriseany material discussed in association with conductive region 108 fromFIGS. 1A-B. Gate electrode 208 may be formed by any technique suitableto provide a conductive region above the top surface of gate dielectriclayer 206 without detrimentally impacting gate dielectric layer 206. Inaccordance with an embodiment of the present invention, gate electrode208 is formed by depositing a blanket film and then subsequentlypatterning the blanket film to form a conductive structure of a desiredshape and dimension. In one embodiment, gate dielectric layer 206 isalso patterned during the patterning of gate electrode 208 to expose thetop surface of substrate 202, as depicted in FIG. 2B. In a specificembodiment, gate dielectric layer 206 is patterned with a wet chemicalcleaning process step that comprises the application of an aqueoussolution of hydrofluoric acid, ammonium fluoride or both. A gateelectrode protection layer 216 may be formed above gate electrode 208,also depicted in FIG. 2B. Gate electrode protection layer 216 maycomprise any material discussed in association with gate electrodeprotection layer 116 from FIG. 1B. In accordance with an embodiment ofthe present invention, gate electrode protection layer 216 is anartifact from the patterning process steps used to for gate electrode208. In an alternative embodiment, gate electrode isolation layer 216 isformed post-patterning above gate electrode 208 by a chemical vapordeposition process.

Referring to FIG. 2C, a pair of sacrificial gate isolation spacers 222may be formed adjacent the sidewalls of gate electrode 208. Sacrificialgate isolation spacers 222 may comprise any material discussed inassociation with gate isolation spacers 118 from FIG. 1B. In accordancewith an embodiment of the present invention, sacrificial gate isolationspacers 222 are used to protect gate electrode 208 during the subsequentsubstrate etch step discussed below. Thus, in an alternative embodiment,gate electrode 208 is robust against the substrate etch step and a pairof sacrificial gate isolation spacers 222 is not required. The pair ofsacrificial gate isolation spacers 222 may be formed by any techniquesuitable to provide total coverage of the sidewalls of gate electrode208. In an embodiment, sacrificial gate isolation spacers 222 are formedby depositing, and subsequently anisotropically etching, a blankeddielectric film. In another embodiment, sacrificial gate isolationspacers 222 are formed by consuming/passivating a portion of gateelectrode 208 in an oxidation process.

FIG. 2C is a cross-sectional view along the A-A′ axis of the top-downview illustrated in FIG. 2C′. As depicted, shallow-trench isolationregions 224 and 226 may be formed in substrate 202. In accordance withan embodiment of the present invention, in order for gate electrode 208and underlying gate dielectric layer 206 to remain in tact during asubsequent substrate etch step, shallow-trench isolation region 226 mustbe present. Isolated devices may also comprise shallow-trench isolationregion 224 and this feature will be included onward for illustrativepurposes. However, it is to be understood that in the case of nestedstructures, shallow-trench isolation region 224 need not be present andsubstrate 202 may be extended along the dashed lines shown in FIG. 2C′.As would be apparent to one of ordinary skill in the art, shallow-trenchisolation regions 224 and 226 would typically have been formed insubstrate 202 prior to the formation of dielectric layer 206. Forexample, in accordance with an embodiment of the present invention,shallow-trench isolation regions 224 and 226 are formed by fillingtrenches created in substrate 202 with a dielectric material, e.g. asilicon dioxide material deposited by a chemical vapor depositionprocess.

Referring to FIG. 2D, a portion of substrate 202 may be removed to forma trench 228 directly between substrate 202, gate dielectric layer 206,and shallow-trench isolation regions 224. A portion of gate dielectriclayer 206, gate electrode 208, sacrificial gate isolation spacers 222and gate electrode protection layer 216 is suspended over trench 228,but another portion of these structures is secured by shallow-trenchisolations regions 226 (shown in FIG. 2C′), as depicted by the dashedlines. Trench 228 may be formed by any technique suitable to selectivelyremove a portion of substrate 202 without significantly impacting gatedielectric layer 206 or gate electrode 208, such as a dry etch or a wetetch process. In accordance with an embodiment of the present invention,gate electrode protection layer 216 and sacrificial gate isolationspacers 222 protect gate electrode 208 during the formation of trench208. In one embodiment, trench 228 is formed by a dry plasma etch steputilizing gases selected from the group consisting of NF₃, HBr, SF₆/Clor Cl₂. In a specific embodiment, portions of substrate 202 are removeduniformly, leaving a trench 228 with equal depth in all locations, asdepicted in FIG. 2D. In another embodiment, a wet etch step utilizingaqueous solutions of NH₄OH or tetramethylammonium hydroxide is used toform trench 228. In one embodiment, these wet etchants are inhibited byhigh density planes of substrate 202 (e.g. the <111> plane in a siliconsubstrate), and trench 228 thus assumes a tapered profile, as depictedin FIG. 2D′. In a specific embodiment, trench 228 is formed by applyingan aqueous solution of NH₄OH with a concentration in the range of 10-30%at a temperature in the range of 20-35 degrees Celsius to a substrate202 comprised of crystalline silicon and a tapered profile results witha surface angle of 55 degrees. For illustrative purposes, however, theuniform trench 228 of FIG. 2D is shown in subsequent steps. Trench 228may be formed to a depth sufficient to remove all channel activity fromsubstrate 202 and/or sufficient to accommodate source/drain regionscomprised of a different semiconductor material, as discussed below. Inone embodiment, trench 228 is formed to a depth in the range of 800-1200Angstroms.

Referring to FIG. 2E, active region 204 is formed in trench 228,directly between substrate 202 and gate dielectric layer 206. Activeregion 204 may be comprised of any material discussed in associationwith active region 104 from FIGS. 1A-B. Additionally, active region 204may incorporate charge-carrier dopant impurity atoms. In one embodiment,active region 204 is a crystalline silicon/germanium active region ofthe stoichiometry Si_(x)Ge_(1-x), where 0≦x≦1, and the charge-carrierdopant impurity atoms are selected from the group consisting of boron,arsenic, indium or phosphorus. In another embodiment, active region 204is comprised of a III-V material and the charge-carrier dopant impurityatoms are selected from the group consisting of carbon, silicon,germanium, oxygen, sulfur, selenium or tellurium. In accordance with anembodiment of the present invention, active region 204 is comprised of asemiconductor material with a composition different than thesemiconductor material of substrate 202 and is compatible withdielectric layer 206.

Active region 204 may be formed by any technique suitable to form ahighly uniform (i.e. low surface defect density, e.g. less than 10⁶dislocations/cm² at the surface of active region 204) crystalline layer.In one embodiment, active region 204 is a uniform epitaxial layer. Inanother embodiment, active region 204 is a graded epitaxial layer,wherein the grading process minimizes surface defects. In an alternativeembodiment, the defect density of active region 204 at the interface ofsubstrate 202 is greater than 10⁸ dislocations/cm², but at the topsurface of active region 204 is less than 10⁵ dislocations/cm². In anembodiment, active region 204 is deposited by a process selected fromthe group consisting of chemical vapor epitaxy, molecular-beam epitaxyor laser-abolition epitaxy. In one embodiment, a wet chemical clean iscarried out immediately prior to the deposition of active region 204. Ina specific embodiment, the wet chemical cleaning process step comprisesthe application of an aqueous solution of hydrofluoric acid, ammoniumfluoride or both.

In the case where sacrificial gate isolation spacers 222 were employedto protect gate electrode 208 during the formation of trench 228 and/orduring the deposition of active region 204, these spacers may be removedfollowing the deposition of active region 204, as depicted in FIG. 2F.In accordance with an embodiment of the present invention, sacrificialgate isolation spacers 222 are removed to enable the optimization of thetip implant step discussed below. In one embodiment, sacrificial gateisolation spacers 222 are removed with a wet chemical cleaning processstep that comprises the application of an aqueous solution ofhydrofluoric acid, ammonium fluoride or both to expose the sidewalls ofgate electrode 208.

Referring to FIG. 2G, a pair of tip extensions 212 may be formed byimplanting charge-carrier dopant impurity atoms into active region 204.The pair of tip extensions 212 may be formed from any of thecharge-carrier dopant impurity atoms discussed in association with thepair of tip extensions 112 from FIG. 1B. In accordance with anembodiment of the present invention, gate electrode 208 acts to mask aportion of active region 204, forming self-aligned tip extensions 212.By self-aligning tip extensions 212 with gate electrode 208, channelregion 214 may be formed in the portion of active region 204 that isunderneath gate electrode 208 and gate dielectric layer 206, as depictedin FIG. 2G. In one embodiment, the charge carrier dopant impurity atomsimplanted to form the pair of tip extensions 212 are of oppositeconductivity to channel region 214. In a specific embodiment, the pairof tip extensions 212 is formed by implanting charge-carrier dopantimpurity atoms with an energy in the range of 0.2 keV-10 keV at a dosein the range of 5E14 atoms/cm²-5E15 atoms/cm² to form a dopantconcentration in the range of 1E20 atoms/cm³-1E21 atoms/cm³ and to adepth in the range of 5-30 nanometers. In order to activate the chargecarrier dopant impurity atoms implanted active region 204 to form thepair of tip extensions 212, any suitable annealing technique may beused. In accordance with an embodiment of the present invention, theannealing technique employed to cause the charge carrier dopant impurityatoms of the pair of tip extensions 212 to become substitutionallyincorporated into the atomic lattice of active region 204 is selectedfrom the group consisting of thermal annealing, laser annealing or flashannealing.

A pair of gate isolation spacers may then be formed. In one embodiment,referring to FIG. 2H, a dielectric material layer 230 is deposited by achemical vapor deposition process and is conformal with the sidewalls ofgate electrode 208 and the top surface of active region 204. Dielectricmaterial layer 230 may be comprised of any of the materials discussed inassociation with the pair of gate isolation spacers 118 from FIG. 1B.Dielectric material layer 230 may be deposited to a thickness selectedto determine the final width of the pair of gate isolation spacers.

Referring to FIG. 21, a pair of gate isolation spacers 218 may be formedfrom dielectric material layer 230 by an anisotropic etch process. Inone embodiment, dielectric material layer 230 is dry etched by a remoteplasma etch or a reactive ion etch process. In another embodiment,dielectric material layer 230 is patterned to form the pair of gateisolation spacers 218 by using a vertical dry or plasma etch processcomprising fluorocarbons of the general formula C_(x)F_(y), where x andy are natural numbers. The pair of gate isolation spacers 218 may sitabove the top surface of active region 204 and may have a width at thetop surface of active region 204 substantially equal to the originalthickness of dielectric material layer 230. In accordance with anembodiment of the present invention, the pair of gate isolation spacers218 resides above the pair of tip extensions 212, as depicted in FIG.21. In one embodiment, the pair of gate isolation spacers 218 forms ahermetic seal with gate electrode 208 and the top surface of activeregion 204 to encapsulate gate dielectric layer 206.

The structure described in association with FIG. 21 may then undergotypical process steps to complete the formation of a MOS-FET, such as animplant step to form a pair of source/drain regions in active region 204and a silicidation step. Alternatively, strain-inducing source/drainregions may be formed in active region 204. Referring to FIG. 2J, a pairof etched-out regions 240 is formed in active region 204 and are alignedwith the outer surfaces of the pair of gate isolation spacers 218,leaving protected the portions of the pair of tip extensions 212 thatare underneath the pair of gate isolation spacers 218. In oneembodiment, gate electrode protection layer 216 protects gate electrode212 during the formation of etched-out regions 240. In accordance withan embodiment of the present invention, etched-out regions 240 areformed to a depth such that substrate 202 is not exposed and in therange of 600-1100 Angstroms. In a specific embodiment, portions ofactive region 204 are removed isotropically, leaving etched-out regions240 with curvature, as depicted in FIG. 2J. In another embodiment, a wetetch step utilizing aqueous solutions of NH₄OH or tetramethylammoniumhydroxide is used to form etched-out regions 240. In one embodiment,these wet etchants are inhibited by high density planes of active region204, and the etched-out regions 240 thus assume a tapered profile. Forillustrative purposes, however, the curved etched-out regions 240 ofFIG. 2J are shown in subsequent steps.

A strain-inducing source/drain region formed in an etched-out portion ofa crystalline semiconductor material may impart a uniaxial strain to thechannel region of the crystalline semiconductor material. In turn, thecrystalline semiconductor material may impart a uniaxial strain to thestrain-inducing source/drain region. In one embodiment, the latticeconstant of the strain-inducing source/drain regions is smaller than thelattice constant of the crystalline semiconductor material and thestrain-inducing source/drain regions impart a tensile uniaxial strain tothe crystalline semiconductor material, while the crystallinesemiconductor material imparts a tensile strain to the strain-inducingsource/drain regions. Thus, when the lattice constant of astrain-inducing source/drain region that fills an etched-out portion ofa crystalline semiconductor material is smaller than the latticeconstant of the crystalline semiconductor material, the lattice-formingatoms of the strain-inducing source/drain region are pulled apart (i.e.tensile strain) from their normal resting state and hence induce atensile strain on the crystalline semiconductor material as they attemptto relax. In another embodiment, the lattice constant of thestrain-inducing source/drain regions is larger than the lattice constantof the crystalline semiconductor material and the strain-inducingsource/drain regions impart a compressive uniaxial strain to thecrystalline semiconductor material, while the crystalline semiconductormaterial imparts a compressive strain to the strain-inducingsource/drain regions. Thus, when the lattice constant of astrain-inducing source/drain region that fills an etched-out portion ofa crystalline semiconductor material is larger than the lattice constantof the crystalline semiconductor material, the lattice-forming atoms ofthe strain-inducing source/drain region are pushed together (i.e.compressive strain) from their normal resting state and hence induce acompressive strain on the crystalline semiconductor material as theyattempt to relax.

Therefore, referring to FIG. 2K, a pair of source/drain regions 220 isformed in etched-out regions 240. The pair of source/drain regions 220may be comprised of any material discussed in association with the pairof source/drain regions 120 from FIG. 1B. Additionally, in accordancewith an embodiment of the present invention, the pair of source/drainregions 220 have a composition different from the composition of thesemiconductor material of active region 204 and impart a uniaxial strainto channel region 214. The pair of source/drain regions 220 may beformed by any technique suitable to form a highly uniform (i.e. lowsurface defect density, e.g. less than 10⁶ dislocations/cm² at thesurface of the pair of source/drain regions 220) crystalline layer. Inone embodiment, the pair of source/drain regions 220 comprises a uniformepitaxial layer. In another embodiment, the pair of source/drain regions220 comprises a graded epitaxial layer, wherein the grading processminimizes surface defects. In an embodiment, the pair of source/drainregions 220 is deposited by a process selected from the group consistingof chemical vapor epitaxy, molecular-beam epitaxy or laser-abolitionepitaxy. In one embodiment, a wet chemical clean is carried outimmediately prior to the deposition of the pair of source/drain regions220. In a specific embodiment, the wet chemical cleaning process stepcomprises the application of an aqueous solution of hydrofluoric acid,ammonium fluoride or both. The pair of source/drain regions 220 mayincorporate charge-carrier dopant impurity atoms. In one embodiment, thepair of source/drain regions 220 is a crystalline silicon/germaniumregion of the stoichiometry Si_(x)Ge_(1-x), where 0≦x≦1, and thecharge-carrier dopant impurity atoms are selected from the groupconsisting of boron, arsenic, indium or phosphorus. In anotherembodiment, the pair of source/drain regions 220 is comprised of a III-Vmaterial and the charge-carrier dopant impurity atoms are selected fromthe group consisting of carbon, silicon, germanium, oxygen, sulfur,selenium or tellurium. The charge-carrier dopant impurity atoms may beincorporated into the pair of source/drain regions 220 at the same timeas the formation of the pair of source/drain regions 220 (i.e. in situ)or as a post ion-implantation step.

The structure described in association with FIG. 2K may then undergotypical process steps to complete the formation of a MOS-FET, such as asilicidation step. Alternatively, subsequent to the formation of thepair of source/drain regions 220, process steps compatible with areplacement gate process scheme may be carried out. In accordance withan embodiment of the present invention, an interlayer dielectric layer250 (e.g. a layer of silicon dioxide) is formed over the pair ofsource/drain regions 220, shallow-trench isolation regions 224, the pairof gate isolation spacers 218 and gate electrode protection layer 216and/or gate electrode 208, as depicted in FIG. 2L. The interlayerdielectric layer 250 may then be polished back and the gate electrodeprotection layer 216 removed with a chemical-mechanical polish step toreveal gate electrode 208, as depicted in FIG. 2M. In one embodiment,gate electrode protection layer 216 acts as a polish-stop layer and awet etch process is subsequently used to remove gate electrodeprotection layer 216 in order to reveal the top surface of gateelectrode 208.

Referring to FIG. 2N, gate electrode 208 may be removed and replacedwith an alternative gate electrode 260. In accordance with an embodimentof the present invention, alternative gate electrode 260 is comprised ofany material described in association with conductive region 108 fromFIGS. 1A-B. Additionally, subsequent to the removal of gate electrode208 and prior to the replacement with alternative gate electrode 260, anadditional dielectric layer 270 may be added to gate dielectric layer206. In accordance with an embodiment of the present invention,additional dielectric layer 270 may be comprised of any materialdiscussed in association with upper layer 106B from FIG. 1B. Theadditional dielectric layer 260 may be formed by an atomic layer orchemical vapor deposition process and may therefore also form on theinner walls of the pair of gate isolation spacers 218, as depicted inFIG. 2N.

Thus, referring to FIG. 2N, a planar MOS-FET comprising an active regionwith a compatible gate dielectric layer may be formed. The planarMOS-FET may be an N-type or a P-type semiconductor device and may beincorporated into an integrated circuit by conventional processingsteps, as known in the art. As will be appreciated in the typicalintegrated circuit, both N- and P-channel transistors may be fabricatedin a single substrate or epitaxial layer to form a CMOS integratedcircuit.

The present invention is not limited to the formation of planar MOS-FETscomprising active regions with compatible gate dielectric layers. Forexample, devices with a three-dimensional architecture, such as tri-gatedevices, may benefit from the above process. As an exemplary embodimentin accordance with the present invention, FIGS. 3A-C illustratecross-sectional views representing the formation of a tri-gate MOS-FEThaving active regions with compatible dielectric layers.

Referring to FIG. 3A, the foundation of a single substrate tri-gateMOS-FET 300 is formed. Tri-gate MOS-FET 300 is comprised of athree-dimensional substrate 302. Three-dimensional substrate 302 may beformed from any material described in association with substrate 102from FIGS. 1A-B. A gate dielectric layer 306 is formed aroundthree-dimensional substrate 302. Gate dielectric layer 306 may be formedfrom any material described in association with dielectric layer 106,lower layer 106A and upper layer 106B from FIGS. 1A-B. A gate electrode308 is formed above gate dielectric layer 306. Gate electrode 308 may beformed from any material described in association with conductive region108 from FIGS. 1A-B. Gate dielectric layer 306 and gate electrode 308may be protected by a pair of gate isolation spacers 318.

Referring to FIG. 3B, a portions of three-dimensional substrate 302 maybe removed to form trench 328. Trench 328 may be formed by any techniquedescribed in association with the formation of trench 228 from FIGS. 2Dand 2D′. Referring to FIG. 3C, three-dimensional active region 304 isformed selectively in trench 328 and on the remaining portion ofthree-dimensional substrate 302. Thus, a method to form a tri-gateMOS-FET device comprising an active region with a compatible gatedielectric layer has been described. The tri-gate MOS-FET may beincorporated into an integrated circuit by conventional processingsteps, as known in the art.

Thus, a method to form a semiconductor structure with an active regionand a compatible dielectric layer has been disclosed. In one embodiment,a semiconductor structure has a dielectric layer comprised of an oxideof a first semiconductor material, wherein a second (and compositionallydifferent) semiconductor material is formed between the dielectric layerand the first semiconductor material. In another embodiment, a portionof the second semiconductor material is replaced with a thirdsemiconductor material in order to impart uniaxial strain to the latticestructure of the second semiconductor material.

What is claimed is:
 1. A method of making a semiconductor structurecomprising: forming a substrate comprising a first semiconductormaterial; forming a dielectric layer above said substrate, wherein saiddielectric layer comprises a layer of oxide of said first semiconductormaterial directly above said substrate; removing a portion of saidsubstrate to form a trench between said dielectric layer and theremaining portion of said substrate; and forming an active region insaid trench, wherein said active region comprises a second semiconductormaterial, wherein the composition of said second semiconductor materialis different from that of said first semiconductor material, and whereinsaid active region is formed directly between said dielectric layer andthe remaining portion of said substrate.
 2. The method of claim 1wherein forming said dielectric layer comprises heating said substratein the presence of an oxidizing agent until a desired thickness of saidlayer of oxide is formed.
 3. The method of claim 2 wherein saidsubstrate is comprised of silicon, wherein said layer of oxide isselected from the group consisting of a layer of silicon dioxide orsilicon oxy-nitride, wherein heating said substrate is carried out at atemperature in the range of 600-800 degrees Celsius for a duration inthe range of 1 minute-1 hour, and wherein said layer of oxide is formedto a thickness in the range of 5-15 Angstroms.
 4. The method of claim 3,further comprising: subsequent to forming said layer of oxide, forming alayer of high-K dielectric material above said layer of oxide, whereinsaid high-K dielectric material is selected from the group consisting ofhafnium oxide, hafnium silicate, lanthanum oxide, zirconium oxide,zirconium silicate, tantalum oxide, barium strontium titanate, bariumtitanate, strontium titanate, yttrium oxide, aluminum oxide, leadscandium tantalum oxide, lead zinc niobate or a combination thereof. 5.The method of claim 1 wherein forming said dielectric layer comprisesforming, in an ALD reaction chamber, a layer of high-K dielectricmaterial above a layer of native silicon dioxide, wherein said high-Kdielectric material is selected from the group consisting of hafniumoxide, hafnium silicate, lanthanum oxide, zirconium oxide, zirconiumsilicate, tantalum oxide, barium strontium titanate, barium titanate,strontium titanate, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate or a combination thereof, and whereinsaid layer of native silicon dioxide has a thickness in the range of3-10 Angstroms.
 6. The method of claim 1 wherein said firstsemiconductor material is comprised of silicon with an atomicconcentration of silicon atoms greater than 97%, and wherein said layerof oxide is selected from the group consisting of a layer of silicondioxide or silicon oxy-nitride.
 7. The method of claim 1 wherein saidsecond semiconductor material is comprised of a material selected fromthe group consisting of gallium nitride, gallium phosphide, galliumarsenide, indium phosphide, indium antimonide, indium gallium arsenide,aluminum gallium arsenide, indium gallium phosphide, germanium orsilicon/germanium with an atomic concentration of germanium atomsgreater than 5%, wherein said first semiconductor material is comprisedof silicon, and wherein said layer of oxide selected from the groupconsisting of is a layer of silicon dioxide or silicon oxy-nitride. 8.The method of claim 1 wherein said dielectric layer further comprises alayer of a high-K dielectric material above said layer of oxide of saidfirst semiconductor material.
 9. The method of claim 8 wherein saidfirst semiconductor material is comprised of silicon, wherein said layerof oxide is selected from the group consisting of a layer of silicondioxide or silicon oxy-nitride, and wherein said high-K dielectricmaterial is selected from the group consisting of hafnium oxide, hafniumsilicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalumoxide, barium strontium titanate, barium titanate, strontium titanate,yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zincniobate or a combination thereof.
 10. A method of making a semiconductordevice comprising: forming a substrate comprising a first semiconductormaterial; forming a gate dielectric layer above said substrate, whereinsaid gate dielectric layer comprises a layer of oxide of said firstsemiconductor material directly above said substrate; forming a gateelectrode above said gate dielectric layer; and, subsequent to formingsaid gate electrode, removing a portion of said substrate to form atrench between said gate dielectric layer and the remaining portion ofsaid substrate; forming an active region in said trench, wherein saidactive region comprises a second semiconductor material, wherein thecomposition of said second semiconductor material is different from thatof said first semiconductor material, and wherein said active region isformed directly between said dielectric layer and the remaining portionof said substrate; forming a pair of tip extensions on either side ofsaid gate electrode and in said active region; forming a pair of gateisolation spacers adjacent to the sidewalls of said gate electrode andabove said pair of tip extensions; and forming a pair of source/drainregions on either side of said pair of gate isolation spacers and insaid active region.
 11. The method of claim 10 wherein forming said gatedielectric layer comprises heating said substrate in the presence of anoxidizing agent until a desired thickness of said layer of oxide isformed.
 12. The method of claim 11 wherein said substrate is comprisedof silicon, wherein said layer of oxide is selected from the groupconsisting of a layer of silicon dioxide or silicon oxy-nitride, whereinheating said substrate is carried out at a temperature in the range of600-800 degrees Celsius for a duration in the range of 1 minute-1 hour,and wherein said layer of oxide is formed to a thickness in the range of5-15 Angstroms.
 13. The method of claim 12, further comprising:subsequent to forming said layer of oxide, forming a layer of high-Kdielectric material above said layer of oxide, wherein said high-Kdielectric material is selected from the group consisting of hafniumoxide, hafnium silicate, lanthanum oxide, zirconium oxide, zirconiumsilicate, tantalum oxide, barium strontium titanate, barium titanate,strontium titanate, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate or a combination thereof.
 14. Themethod of claim 10 wherein forming said dielectric layer comprisesforming, in an ALD reaction chamber, a layer of high-K dielectricmaterial above a layer of native silicon dioxide, wherein said high-Kdielectric material is selected from the group consisting of hafniumoxide, hafnium silicate, lanthanum oxide, zirconium oxide, zirconiumsilicate, tantalum oxide, barium strontium titanate, barium titanate,strontium titanate, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate or a combination thereof, and whereinsaid layer of native silicon dioxide has a thickness in the range of3-10 Angstroms.
 15. The method of claim 10 wherein forming said pair ofsource/drain regions comprises removing a portion of said active regionto form a pair of trenches in said active region and forming a thirdsemiconductor material in said pair of trenches, and wherein thecomposition of said third semiconductor material is different from thatof said second semiconductor material.
 16. The method of claim 10,further comprising: subsequent to forming said pair of source/drainregions, forming an inter-layer dielectric layer above said pair ofsource/drain regions, above said pair of gate isolation spacers andabove said gate electrode; polishing said inter-layer dielectric layerto expose the top surface of said gate electrode; removing said gateelectrode to provide a trench between said pair of gate isolationspacers; and forming a metal layer in said trench to form a metal gateelectrode.
 17. The method of claim 16, further comprising: subsequent toremoving said gate electrode and prior to forming said metal gateelectrode, forming a layer of a high-K dielectric material directlyabove said gate dielectric layer.
 18. The method of claim 10, furthercomprising: prior to removing said portion of said substrate, forming apair of sacrificial gate isolation spacers adjacent to the sidewalls ofsaid gate electrode; and prior to forming said pair of tip extensions oneither side of said gate electrode, removing said pair of sacrificialgate isolation spacers.
 19. The method of claim 10 wherein said firstsemiconductor material is comprised of silicon with an atomicconcentration of silicon atoms greater than 97%, and wherein said layerof oxide is selected from the group consisting of a layer of silicondioxide or silicon oxy-nitride.
 20. The method of claim 10 wherein saidsecond semiconductor material is comprised of a material selected fromthe group consisting of gallium nitride, gallium phosphide, galliumarsenide, indium phosphide, indium antimonide, indium gallium arsenide,aluminum gallium arsenide, indium gallium phosphide, germanium orsilicon/germanium with an atomic concentration of germanium atomsgreater than 5%, wherein said first semiconductor material is comprisedof silicon, and wherein said layer of oxide is selected from the groupconsisting of a layer of silicon dioxide or silicon oxy-nitride.
 21. Themethod of claim 10 wherein said gate dielectric layer further comprisesa layer of a high-K dielectric material above said layer of oxide ofsaid first semiconductor material.
 22. The method of claim 21 whereinsaid first semiconductor material is comprised of silicon, wherein saidlayer of oxide is selected from the group consisting of a layer ofsilicon dioxide or silicon oxy-nitride, and wherein said high-Kdielectric material is selected from the group consisting of hafniumoxide, hafnium silicate, lanthanum oxide, zirconium oxide, zirconiumsilicate, tantalum oxide, barium strontium titanate, barium titanate,strontium titanate, yttrium oxide, aluminum oxide, lead scandiumtantalum oxide, lead zinc niobate or a combination thereof.
 23. A methodof making a semiconductor device comprising: forming a substratecomprising a first semiconductor material; forming a gate dielectriclayer above said substrate; forming a gate electrode above said gatedielectric layer; and, subsequent to forming said gate electrode,removing a portion of said substrate to form a trench between said gatedielectric layer and the remaining portion of said substrate; forming anactive region in said trench, wherein said active region comprises asecond semiconductor material, wherein the composition of said secondsemiconductor material is different from that of said firstsemiconductor material, and wherein said active region is formeddirectly between said dielectric layer and the remaining portion of saidsubstrate; forming a pair of tip extensions on either side of said gateelectrode and in said active region; forming a pair of gate isolationspacers adjacent to the sidewalls of said gate electrode and above saidpair of tip extensions; and forming a pair of source/drain regions oneither side of said pair of gate isolation spacers and in said activeregion, wherein said pair of source/drain regions is comprised of athird semiconductor material, and wherein the composition of said thirdsemiconductor material is different from that of said secondsemiconductor material.
 24. The method of claim 23 wherein the atomicconcentration of silicon atoms in said first semiconductor material isgreater than 97%.
 25. The method of claim 24 wherein said secondsemiconductor material is comprised of a material selected from thegroup consisting of gallium nitride, gallium phosphide, galliumarsenide, indium phosphide, indium antimonide, indium gallium arsenide,aluminum gallium arsenide, indium gallium phosphide, germanium orsilicon/germanium with an atomic concentration of germanium atomsgreater than 5%.
 26. The method of claim 23, wherein said gatedielectric layer is comprised of a material selected from the groupconsisting of silicon dioxide, silicon oxy-nitride, hafnium oxide,hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate,tantalum oxide, barium strontium titanate, barium titanate, strontiumtitanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide,lead zinc niobate or a combination thereof.